As is known in the art, syringes are medical delivery devices utilizable to administer a medicament to a patient. Syringes are normally marketed either in prefilled form, wherein a set dosage of medicament is already provided therein, or they are empty and intended to be filled from a vial or other source of medicament by an end user at the time administration of the medicament is desired.
Syringes typically include a barrel portion adapted to retain the medicament. The distal end of the barrel is normally configured to mate with a conventional piercing element, such as a pointed needle cannula made of steel or like material or a blunt ended cannula formed of plastic, to deliver the medicament contained in the barrel. A plunger rod is inserted through the open distal end of the syringe barrel and, through its engagement with an elastomeric or rubber-like stopper element fitted in a fluid-tight manner within the interior of the barrel, a user can apply manual force to the plunger to deliver the medicament through the piercing element. A flange is also typically provided around the open distal end of the syringe barrel as a form of finger rest to facilitate a user's manipulation of the device.
As the skilled artisan will appreciate, one problem with either pre-filled syringes or empty syringes is that the stopper element can be inadvertently dislodged from the syringe barrel, rendering the syringe itself unusable and/or the medicament therein unsterile. For instance, particularly in the case of prefilled syringes, forces exerted on the stopper during terminal sterilization procedures could cause the stopper to eject from the open distal end of the syringe, rendering the product unusable. Also, end users attempting to aspirate medicament through the piercing element into the syringe barrel could, inadvertently, exert excess force onto the plunger, causing the stopper to dislodge from the barrel. There is also the risk that for certain medicaments, such as cytotoxic drugs, that safety concerns dictate that the stopper not be dislodged from the barrel.
Numerous attempts in the art have sought to address the aforementioned concerns. For instance, U.S. Pat. No. 4,711,637 to Leigh et at. describes a syringe lock formed as a clip made from a malleable material such as sheet metal. The clip, affixed to the proximal end of the syringe, includes a protrusion jutting towards the interior portion of the barrel which serves to "bite" into the plunger so as to arrest movement thereof once a desired plunger position is achieved. In this type of device, inadvertent rotation of the plunger could cause unwanted locking, rendering the syringe unusable. Another clip-type approach is found in U.S. Pat. No. 4,883,471 to Braginetz et al., wherein a spring clip is disposed around the exterior of the syringe barrel. The clip includes finger elements protruding through apertures formed in the syringe barrel. The finger elements physically arrest the stopper element once a desired plunger extension is reached.
Alternately, structure may be incorporated as part of the syringe barrel itself to physically restrain the syringe stopper from inadvertent withdrawal. Examples of these approaches are found, inter alia, in U.S. Pat. No. 4,946,441 to Laderoute and European Patent Application No. 0 409 134 to Escudero. These approaches are oftentimes uneconomical in that costly modifications will be required to molding equipment to achieve the desired structure. In addition, by employing specific, integral syringe barrel construction, the user is deprived of the ability to effect easy, intentional removal of the stopper by disabling the stopper lock structure, if such action is desired.
PCT Application WO 94/26334 discloses, inter alia, two embodiments of a plunger lock device for a syringe. A first embodiment is of the spring clip type and includes a finger portion 61 jutting into the interior of the syringe barrel. The finger portion 61 physically arrests the stopper from inadvertent withdrawal. A second embodiment entails a disk-like addition which mounts to the flange area of the syringe. The top portion of the disk includes an aperture, aligned with the syringe barrel, that is smaller than the internal diameter of the barrel. While the smaller diameter disk aperture prevents the stopper from inadvertent withdrawal, this embodiment can only be effected where the disk is first mounted to the syringe flange and the plunger thereafter inserted through the disk aperture for attachment to the stopper. Accordingly, the disk device as taught therein is mainly intended for use where it is shipped intact with a fully assembled syringe, and most likely where affixation of the plunger lock device is part of the syringe filling, assembly and/or sterilization processes. Most syringe processing machinery, however, is not set up to accommodate manipulation of the lock device, and modifications to the production line can be costly if not difficult. For reasons of economy, and particularly where specialized filling or sterilization machinery is already in place, it would be advantageous to ship the device apart from a pre-filled or pre-assembled syringe for later affixation. Moreover, it would also be advantageous to permit affixation of the brake device as an add-on component, without having to disrupt the plunger from the stopper.